Impedance matching apparatus

ABSTRACT

An impedance matching apparatus  3  calculates a forward wave voltage Vfo and a reflected wave voltage Vro at an output terminal  3   b , based on a forward wave voltage Vfi and a reflected wave voltage Vri at an input terminal  3   a , on information on variable values of variable capacitors VC 1 , VC 2  acquired in advance through measurement, and on a T parameter of the impedance matching apparatus  3  corresponding to the information on the variable values of variable capacitors VC 1 , VC 2 . The impedance matching apparatus  3  calculates an input reflection coefficient Γi at the input terminal  3   a  corresponding to the information on the variable values of the variable capacitors VC 1 , VC 2 , based on the forward wave voltage Vfo, the reflected wave voltage Vro and the T parameter. The impedance matching apparatus  3  selects the lowest absolute value out of absolute values |Γi| of the input reflection coefficients corresponding to the variable values of the variable capacitors VC 1 , VC 2 , and adjusts the impedance of the variable capacitors VC 1 , VC 2  based on the lowest value.

This application is a division of U.S. Ser. No. 11/263,636, filed Oct.31, 2005, which application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an impedance matching apparatus to beinterposed between a high-frequency power source and a load, formatching the impedance of the high-frequency power source and theimpedance of the load.

2. Description of the Related Art

Manufacturing process of semiconductors or flat panel displays includesa plasma process. Some of plasma process chambers to be employed in theplasma process require to be applied to high-frequency voltage with aradio frequency band, for example, from 100 kHz to 300 MHz.

Between the high-frequency power source and the plasma process chamberacting as the load, an impedance matching apparatus is interposed. Theimpedance matching apparatus serves to match the impedance of thehigh-frequency power source and that of the plasma process chamber i.e.the load, to minimize the reflected power from the load to thehigh-frequency power source, thus maximizing the power supply to theload.

FIG. 10 depicts a configuration of a high-frequency power supply systemincluding an impedance matching apparatus, disclosed in JP-A H05-63604.The impedance matching apparatus according to the cited document, has aninput terminal connected to a high-frequency power source 41, and anoutput terminal connected to a load 42. The impedance matching apparatusincludes a matching circuit 43 including an input-side detector 44,inductors L2, L3 and variable capacitors VC3, VC4 serving as impedancevariable devices.

The input-side detector 44 detects a high-frequency voltage V and ahigh-frequency current I with a radio frequency band, and a phasedifference θ between the high-frequency voltage V and the high-frequencycurrent I. The detected high-frequency voltage V, high-frequency currentI and the phase difference θ therebetween are input to a computer 46 viaan A/D converter 45 separately provided from the impedance matchingcircuit 43.

The computer 46 calculates an input impedance Zi of the impedancematching circuit 43, i.e. the impedance Zi present in the impedancematching circuit 43 in a direction from the input terminal 43 a towardthe load 42, based on the results detected by the input-side detector 44(i.e. high-frequency voltage V, high-frequency current I, phasedifference θ).

Each of the variable capacitors VC3, VC4 includes an adjustment unit(not shown) to change the capacitance of the variable capacitor VC3 andVC4, respectively, controlled by a motor M when a control signal outputfrom the computer 46 is input to the driving voltage supplier 47 so asto drive the motor M. The computer 46 detects the adjustment positionsof the variable capacitors VC3, VC4, to thereby calculate the impedancesZc3, Zc4 of the variable capacitors VC3, VC4 serving as the impedancevariable devices.

The computer 46 calculates a load circuit-side impedance Zo at theoutput terminal 43 b of the impedance matching circuit 43 in a directiontoward the load 42, based on the input impedance Zi and the impedancesZc3, Zc4 of the impedance variable devices.

The computer 46 varies the adjustment positions of the variablecapacitors VC3, VC4 so that the input impedance Zi matches with theoutput impedance Zp (for instance, 50Ω) on the side of thehigh-frequency power source 41 based on the calculated load circuit-sideimpedance Zo, thus matching the impedance of the high-frequency powersource 41 and that of the load 42.

The impedance matching circuit 43 according to the cited documentacquires the load circuit-side impedance Zo based on the input impedanceZi calculated from the high-frequency voltage V, the high-frequencycurrent I, and the phase difference θ therebetween detected by theinput-side detector 44, and on the impedances Zc3, Zc4 of the variablecapacitors VC3, VC4 detected by the computer 46 with regard to theadjustment positions of the variable capacitors VC3, VC4, and thendetermines the adjustment positions of the variable capacitors VC3, VC4to be matched.

When handling a high-frequency wave, however, the circuit devicesserving as the matching circuit of the impedance matching circuit 43include not only the variable capacitors VC3, VC4 and the inductors L2,L3, but also stray capacitance components between those parts and thehousing and inductance components of copper plates or waveguidesconnecting those parts, and influences such impedance components isunable to disregard on the impedance matching performance.

The impedance controlling method according to the cited document employsthe impedance matching circuit 43 consisting only of the variablecapacitors, VC3, VC4 and the inductors L2, L3, so as to determinematching characteristics of the matching circuit at the currentadjustment positions, based on the impedance values Zc3, Zc4 of thevariable capacitors VC3, VC4 at the current adjustment positions, and onimpedance values Z13, Z14 of the inductors L2, L3. Accordingly, from astrict viewpoint, the impedance components such as the stray capacitanceare not counted in the matching circuit, and hence the matching circuitis not designed to perform in consideration of the impedance componentssuch as the stray capacitance. As a result, the matching circuitaccording to the cited document fails to perform with sufficientaccuracy, especially in a high-frequency region.

Also, the impedance components such as the stray capacitance readilychange depending on the shape of the housing around the impedancematching circuit 43, or on the positional relation inside the impedancematching circuit 43 of the parts such as the variable capacitors VC3,VC4, the inductors L2, L3, and the other parts, and the wirings.Therefore, the matching circuits including the impedance components suchas the stray capacitance may have different characteristics depending onthe internal structure of the matching apparatus, even though thematching circuits are constituted of the same variable capacitors VC3,VC4 and the inductors L2, L3, and hence may suffer from the problem ofunequal matching accuracy among the apparatuses.

SUMMARY OF THE INVENTION

The present invention has been conceived in view of such situation, withan object to solve the foregoing problems.

A first aspect of the present invention provides an impedance matchingapparatus to be interposed between a high-frequency power source and aload, for changing an impedance of an impedance variable device so as tomatch an impedance of the high-frequency power source and an impedanceof the load, comprising: a high-frequency wave information detector todetect information on a forward wave advancing from the high-frequencypower source toward the load and information on a reflected waveadvancing from the load toward the high-frequency power source, at aninput terminal of the impedance matching apparatus; a variable deviceinformation detector to detect information on a variable value of theimpedance variable device; a first storage unit to store therein acharacteristic parameter of the impedance matching apparatus acquiredthrough a preceding measurement, with respect to the information on avariable value of a plurality of the impedance variable devices, incorrelation with the information on the variable value of the impedancevariable device; a first calculator to calculate the information on theforward wave and the information on the reflected wave at an outputterminal of the impedance matching apparatus, based on the informationon the variable value of the impedance variable device detected by thevariable device information detector, on the characteristic parameterstored in the first storage unit, and on the information on the forwardwave and the information on the reflected wave detected by thehigh-frequency wave information detector; a second calculator tocalculate an input reflection coefficient at the input terminal of theimpedance matching apparatus with respect to the information on thevariable value of a plurality of the impedance variable devices, basedon the information on the forward wave and the information on thereflected wave at the output terminal of the impedance matchingapparatus calculated by the first calculator and on a plurality of thecharacteristic parameters stored in the first storage unit; a secondstorage unit to store therein a plurality of input reflectioncoefficients calculated by the second calculator in correlation with theinformation on the variable value of the impedance variable device; afirst identifier to select an input reflection coefficient closest to apredetermined target input reflection coefficient out of the pluralityof input reflection coefficients stored in the second storage unit, andto identify the information on the variable value of the impedancevariable device corresponding to the selected input reflectioncoefficient; and an adjustment unit to adjust an impedance of theimpedance variable device, based on the information on the variablevalue of the impedance variable device identified by the firstidentifier.

Preferably, the second calculator may calculate the information on theforward wave and the information on the reflected wave at the inputterminal of the impedance matching apparatus with respect to theinformation on the variable value of a plurality of the impedancevariable devices, based on the information on the forward wave and theinformation on the reflected wave at the output terminal of theimpedance matching apparatus calculated by the first calculator and onthe plurality of characteristic parameters stored in the first storageunit, and may calculate the input reflection coefficient with respect tothe information on the variable value of the plurality of impedancevariable devices, based on the calculated information on the forwardwave and, the information on the reflected wave at the input terminal ofthe impedance matching apparatus.

Preferably, the impedance matching apparatus may further comprise asetting unit to set the target input reflection coefficient.

Preferably, the characteristic parameter may be an S parameter, or a Tparameter acquired through conversion from the S parameter.

A second aspect of the present invention provides an impedance matchingapparatus to be interposed between a high-frequency power source and aload, for changing an impedance of an impedance variable device so as tomatch an impedance of the high-frequency power source and an impedanceof the load, comprising: a high-frequency wave information detector todetect information on a forward wave advancing from the high-frequencypower source toward the load and information on a reflected waveadvancing from the load toward the high-frequency power source, at aninput terminal of the impedance matching apparatus; a variable deviceinformation detector to detect information on a variable value of theimpedance variable device; a first storage unit to store therein acharacteristic parameter of the impedance matching apparatus acquiredthrough a preceding measurement, with respect to the information on thevariable value of a plurality of the impedance variable devices, incorrelation with the information on the variable value of the impedancevariable device; a first calculator to calculate the information on theforward wave and the information on the reflected wave at an outputterminal of the impedance matching apparatus, based on the informationon the variable value of the impedance variable device detected by thevariable device information detector, on the characteristic parameterstored in the first storage unit, and on the information on the forwardwave and the information on the reflected wave detected by thehigh-frequency wave information detector; a third calculator tocalculate a reflection coefficient at the output terminal of theimpedance matching apparatus, based on the information on the forwardwave and the information on the reflected wave at the output terminal ofthe impedance matching apparatus calculated by the first calculator; afourth calculator to calculate a reflection coefficient at the outputterminal of the impedance matching apparatus with respect to theinformation on the variable value of the plurality of impedance variabledevices, based on a predetermined target input reflection coefficientand a plurality of the characteristic parameters stored in the firststorage unit; a third storage unit to store therein a plurality of thereflection coefficients calculated by the fourth calculator incorrelation with the information on the variable value of the impedancevariable device; a second identifier to select a reflection coefficientclosest to the reflection coefficient at the output terminal of theimpedance matching apparatus calculated by the third calculator out ofthe plurality of reflection coefficients stored in the third storageunit, and to identify the information on the variable value of theimpedance variable device corresponding to the selected reflectioncoefficient; and an adjustment unit to adjust an impedance of theimpedance variable device, based on the information on the variablevalue of the impedance variable device identified by the secondidentifier.

Preferably, the impedance matching apparatus may further comprise asetting unit to set the target input reflection coefficient.

Preferably, the characteristic parameter may be an S parameter, or a Tparameter acquired through conversion from the S parameter.

Other features and benefits of the present invention will become moreapparent from the description on exemplary embodiments given here below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a high-frequencypower supply system including an impedance matching apparatus accordingto the first embodiment of the present invention, and a circuit diagramof the impedance matching apparatus.

FIG. 2 is a table showing S parameter data corresponding to adjustmentpositions of variable capacitors stored in the EEPROM.

FIG. 3 is a block diagram showing a configuration for measuring Sparameters of the impedance matching apparatus.

FIG. 4 is a block diagram showing functional blocks of the control unit.

FIG. 5 is a flowchart showing an operating process of the impedancematching apparatus.

FIG. 6 is a diagram schematically showing combinations of the adjustmentpositions of the variable capacitors.

FIG. 7 is a block diagram showing functional blocks of the control unitof an impedance matching apparatus according the second embodiment ofthe present invention.

FIG. 8 is a flowchart showing an operating process of the impedancematching apparatus according to the second embodiment.

FIG. 9 is a graph showing UV coordinates for selecting a reflectioncoefficient closest to the output reflection coefficient.

FIG. 10 is a block diagram showing a configuration of a high-frequencypower supply system including a conventional impedance matchingapparatus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, embodiments of the present invention will be described indetails, referring to the accompanying drawings.

FIG. 1 is a block diagram showing a configuration of a high-frequencypower supply system including an impedance matching apparatus accordingto the first embodiment of the present invention, and a circuit diagramof the impedance matching apparatus.

The high-frequency power supply system supplies a high-frequency wave toan object to be processed such as a semiconductor wafer or a liquidcrystal substrate, to thereby perform a processing such as plasmaetching. The high-frequency power supply system includes ahigh-frequency power source 1, a transmission line 2, an impedancematching apparatus 3, a load connector 4 and a load 5 including a plasmaprocessing apparatus (plasma process chamber).

The high-frequency power source 1 supplies a high-frequency power with apredetermined frequency (for instance, 13.56 MHz or 200 MHz) to the load5. The high-frequency power source 1 is connected to the impedancematching apparatus 3 via the transmission line 2, which is for example acoaxial cable. The impedance matching apparatus 3 is connected to theload connector 4 including for example a shielded copper plate thatserves to suppress leakage of electromagnetic waves, and the loadconnector 4 is connected to the load 5.

The load 5 is a plasma processing apparatus that performs an etching ora CVD for processing a semiconductor wafer or a liquid crystalsubstrate. The plasma processing apparatus performs various types ofworks depending on the processing purpose of the object. When performingan etching on the object for example, the plasma processing apparatusappropriately determines the type of gas, the gas pressure, the amountto be supplied, and the supplying time of the high-frequency power,depending on the etching process to be performed. In the plasmaprocessing apparatus, the gas to be used for plasma discharge isintroduced into a container (not shown) in which the object is placed,and plasma discharge is performed with the gas thus to turn the gascondition from a non-plasma state into a plasma state. And then, the gasin the plasma state is utilized for processing the object.

The impedance matching apparatus 3 serves to match the impedance of thehigh-frequency power source 1 connected to the input terminal 3 athereof and the impedance of the load 5 connected to the output terminal3 b thereof. To be more detailed, for example, when the impedance in adirection from the input terminal 3 a toward the high-frequency powersource 1 (output impedance) is designed to be 50Ω and the high-frequencypower source 1 is connected to the input terminal of the impedancematching apparatus 3 via the transmission line 2 having a characteristicimpedance of 50Ω, the impedance matching apparatus 3 automaticallyadjusts the impedance in a direction from the input terminal 3 a of theimpedance matching apparatus 3 toward the load 5 to be as close aspossible to 50Ω. It is to be noted that although the characteristicimpedance is specified as 50Ω in this embodiment, the characteristicimpedance is not limited to 50 Ω.

The impedance matching apparatus 3 includes a directional coupler 6, acontrol unit 9, an inductor L1, and variable capacitors VC1, VC2 servingas impedance variable devices. The inductor L1 and the variablecapacitors VC1, VC2 constitute a matching circuit.

The directional coupler 6 separately detects a high-frequency waveadvancing from the high-frequency power source 1 toward the load 5(hereinafter, “forward wave”) and a high-frequency wave reflected fromthe load 5 (hereinafter, “reflected wave”). The directional coupler 6includes, for example, an input port 6 a and three output ports 6 b, 6c, 6 d, and the input port 6 a is connected to the high-frequency powersource 1 while the first output port 6 b is connected to the variablecapacitors VC1, VC2. The second output port 6 c and the third outputport 6 d are connected to the control unit 9. The directional coupler 6works as a part of the high-frequency wave information detectoraccording to the present invention.

The forward wave input through the input port 6 a is output through thefirst output port 6 b, and the reflected wave input through the firstoutput port 6 b is output through the input port 6 a. The forward waveis attenuated to an appropriate level to be detected, and is outputthrough the second output port 6 c. The reflected wave is attenuated toan appropriate level to be detected, and output through the third outputport 6 d.

Here, an input-side detector may be employed instead of the directionalcoupler 6. The input-side detector serves to detect, for example, ahigh-frequency voltage and a high-frequency current input to the inputterminal 3 a from the high-frequency power source 1, and a phasedifference therebetween. The high-frequency voltage, the high-frequencycurrent and the phase difference detected by the input-side detector areinput to the control unit 9.

The control unit 9 acts as the control center of the impedance matchingapparatus 3, and includes a CPU, RAM, ROM and so forth though not shown.The control unit 9 changes the capacitances C1, C2 of the variablecapacitors VC1, VC2 based on outputs of the directional coupler 6, so asto control the automatic matching operation of the impedance matchingapparatus 3.

The control unit 9 outputs control signals to the variable capacitorsVC1, VC2, to achieve impedance matching between the high-frequency powersource 1 and the load 5. The variable capacitors VC1, VC2 change theareas of their pairs of facing electrodes (not shown) based on thecontrol signals from the control unit 9, to thereby vary thecapacitances C1, C2 of the variable capacitors VC1, VC2. Specifically,the variable capacitors VC1, VC2 respectively include adjustment units11, 12 that change the capacitances C1, C2.

Each of the adjustment units 11, 12 includes a stepping motor fordriving the pair of facing electrodes and a motor driving circuit(neither shown). The control unit 9 controls the rotation amounts of thestepping motors thus to change the capacitances C1, C2 of the variablecapacitors VC1, VC2. In this embodiment, the capacitances C1, C2 of thevariable capacitors VC1, VC2 are set to be variable in a thousand steps.The adjustment units 11, 12 serve as adjusting means in the presentinvention.

The variable capacitors VC1, VC2 respectively include position detectors13, 14 that detect adjustment positions changed by the adjustment units11, 12. Position information of the variable capacitors VC1, VC2detected by the position detectors 13, 14 is input to the control unit9, to be recognized by the control unit 9.

The position detectors 13, 14 serve as detecting means in the presentinvention for information about the variable devices. Also, theinformation on the variable values of the impedance variable devicesaccording to the present invention refers to the information thatenables to identify the variable value of the impedance variable devicessuch as the variable capacitors VC1, VC2.

Though the position information of the stepping motors is employed asthe variable values of the impedance variable devices in thisembodiment, the variable values of the impedance variable devices doesnot have to be limited to employ it, and with motors of different typessuch as servomotors, they may employ the position information of suchmotors. Also, the position information may be represented by numbers ofsteps of stepping motors, or by other indices such as numbers of pulsesor voltages. Thus, it is adequate to employ such information that allowsdirectly or indirectly to specify the variable values of the impedancevariable devices.

The control unit 9 is connected to an EEPROM 15. In the EEPROM 15,scattering parameter (hereinafter, “S parameter”) data of the impedancematching apparatus 3 at each of the adjustment positions of the variablecapacitors VC1, VC2 are stored. The S parameter data at each of theadjustment positions of the variable capacitors VC1, VC2 are measuredfor example in the factory in advance of the shipment of the products.Such data may be stored in a non-volatile memory such as a flash memory,instead of in the EEPROM 15. The EEPROM 15 serves as the first storageunit in the present invention.

It is to be noted that S parameters represent, as are generally known,transmission characteristics in a predetermined 4-terminal circuitnetwork obtained when a high-frequency signal is input to an inputterminal and an output terminal of the 4-terminal circuit networkconnected to a line having a characteristic impedance (for instance,50Ω). More specifically, S parameters are input-side voltage reflectioncoefficient (S₁₁), forward voltage transmission coefficient (S₂₁),reverse voltage transmission coefficient (S₁₂), and output-side voltagereflection coefficient (S₂₂), constituting a matrix as indicated byFormula 1 given below. In this embodiment, the impedance matchingapparatus 3 is regarded as the 4-terminal circuit network, forcalculating S parameters of the impedance matching apparatus 3.$\begin{matrix}\begin{bmatrix}S_{11} & S_{12} \\S_{21} & S_{22}\end{bmatrix} & (1)\end{matrix}$

As shown in FIG. 2, in the EEPROM 15 a set of S parameters is storedwith respect to every adjustment positions of the variable capacitorsVC1, VC2. According to FIG. 2, a set of S parameters are represented by[SXY(X=0, 1, . . . , 999, Y=0, 1, . . . 999)], such that, for example,when the adjustment position of the variable capacitor VC1 is “0” andthe adjustment position of the variable capacitor VC2 is “0”, the set ofS parameters is expressed as “S00”.

The data of the set “S00” include, as shown by Formula 1, suchparameters as the input-side voltage reflection coefficient (S₁₁), theforward voltage transmission coefficient (S₂₁), the reverse voltagetransmission coefficient (S₁₂), and the output-side voltage reflectioncoefficient (S₂₂). The parameter sets with respect to every adjustmentpositions of the variable capacitors VC1, VC2 have unique values.

The control unit 9 calculates a voltage Vfo of the forward wave and avoltage Vro of the reflected wave at the output terminal 3 b of theimpedance matching apparatus 3, based on the transmission parameters(hereinafter, T parameters) computed through conversion from the Sparameters stored in the EEPROM 15 and on outputs of the directionalcoupler 6 (more specifically, vector information computed throughconversion at a vectorization unit 21 to be described later).

The control unit 9 calculates the absolute values |Γ| of the inputreflection coefficients Γi at the input terminal 3 a with respect to allof the combinations of the adjustment positions of the variablecapacitors VC1, VC2, based on the forward wave voltage Vfo and thereflected wave voltage Vro at the output terminal 3 b. The control unit9 selects the smallest absolute value |Γ| of the input reflectioncoefficient Γi from all of the absolute values |Γ| of the inputreflection coefficients Γi, and determines which adjustment positions ofthe variable capacitors VC1, VC2 should be adopted based on the smallestabsolute value |Γ| of the input reflection coefficient Γi. Details ofsuch controlling process will be subsequently described.

FIG. 3 is a block diagram showing a configuration of a measuring circuitfor acquiring S parameter data of the impedance matching apparatus 3.The measuring circuit is assembled, for example in a factory, in advanceof the shipment of the products.

According to FIG. 3, S parameter data of the impedance matchingapparatus 3 are acquired for example through a network analyzer 20having an input/output (hereinafter, I/O) impedance of 50Ω. Morespecifically, the first I/O terminal 20 a of the network analyzer 20 isconnected to the input terminal 3 a of the impedance matching apparatus3, and the second I/O terminal 20 b of the network analyzer 20 isconnected to the output terminal 3 b of the impedance matching apparatus3. Likewise, a control terminal 20 c of the network analyzer 20 isconnected to the control unit 9 of the impedance matching apparatus 3.

The measuring circuit thus configured acquires S parameter data asfollows.

As already stated, the variable capacitors VC1, VC2 are adjustable inmultiple steps, and S parameters of the impedance matching apparatus 3are acquired with respect to each single step of the adjustmentpositions of the variable capacitors VC1, VC2, by the network analyzer20.

To be more detailed, firstly the control unit 9 sets the adjustmentpositions of the variable capacitors VC1, VC2 at (0, 0), for instance.Then a high-frequency wave (for instance, 13.56 MHz or 200 MHz) is inputto the input terminal 3 a of the impedance matching apparatus 3, fromthe first I/O terminal 20 a of the network analyzer 20. Here, thefrequency of the high-frequency wave is the frequency of thehigh-frequency power supplied by the high-frequency power source 1 tothe load 5, in the high-frequency power supply system.

The high-frequency wave output from the network analyzer 20 (i.e.incident wave) is partially reflected at the input terminal 3 a of theimpedance matching apparatus 3, and is input to the network analyzer 20through the first I/O terminal 20 a. (Hereinafter, the reflected part isreferred to as “reflected wave”.) The rest of the incident wave istransmitted through the impedance matching apparatus 3, and is outputthrough the output terminal 3 b, and then is input to the networkanalyzer 20 through the second I/O terminal 20 b. (Hereinafter, thetransmitted part is referred to as “transmitted wave”.)

The reflected wave and the transmitted wave are respectively detectedinside the network analyzer 20, so that the input-side voltagereflection coefficient (S₁₁) and the forward voltage transmissioncoefficient (S₂₁) constituting a part of the set of S parameters aremeasured based on the incident wave, the reflected wave and thetransmitted wave. Specifically, when the incident wave, the reflectedwave, and the transmitted wave are denoted by a1, b1, and b2respectively, the voltage reflection coefficient (S₁₁) and the forwardvoltage transmission coefficient (S₂₁) can be measured throughcalculation of S₁₁=b1/a1 and S₂₁=b2/a1.

Then a high-frequency wave having the same frequency is input to theoutput terminal 3 b of the impedance matching apparatus 3 from thesecond I/O terminal 20 b of the network analyzer 20. The high-frequencywave output from the network analyzer 20 (i.e. incident wave) ispartially reflected at the output terminal 3 b of the impedance matchingapparatus 3, and is input to the network analyzer 20 through the secondI/O terminal 20 b. The rest of the incident wave is transmitted throughthe impedance matching apparatus 3, and is output through the inputterminal 3 a, and then is input to the network analyzer 20 through thefirst I/Q terminal 20 a.

The reflected wave and the transmitted wave are respectively detectedinside the network analyzer 20, so that the reverse voltage transmissioncoefficient (S₁₂) and the output-side voltage reflection coefficient(S₂₂) constituting a part of the set of S parameters are measured basedon the incident wave, the reflected wave, and the transmitted wave.Specifically, when the incident, wave, the reflected wave, and thetransmitted wave are denoted by a2, b2, and b1 respectively, the voltagereflection coefficient (S₁₂) and the reverse voltage transmissioncoefficient (S₂₂) can be measured through calculation of S₁₂=b1/a2 andS₂₂=b2/a2.

Thereafter, the control unit 9 changes the adjustment positions of thevariable capacitors VC1, VC2 in an increment of each single step, andthe S parameters with respect to the respective changed adjustmentpositions are similarly measured.

The network analyzer 20 then outputs a plural of data sets, respectivelyincluding an adjustment position of the variable capacitor VC1, anadjustment position of the variable capacitor VC2, and a set of Sparameters, to the control unit 9. The control unit 9 sequentiallystores the data sets in the EEPROM 15. Accordingly, the EEPROM 15clarifies correspondence between the adjustment positions of thevariable capacitors VC1, VC2 and the S parameters on storing, as shownin FIG. 2.

Here, together with the set of S parameters, the capacitances C1, C2 ofthe variable capacitors VC1, VC2 may be stored in the EEPROM 15 insteadof the position information of the stepping motors to change thecapacitances C1, C2 of the variable capacitors VC1, VC2. When employingservo motors in place of the stepping motors, the EEPROM 15 may clarifycorrespondence between the position information of the servo motors andthe S parameters on storing.

The number of the data sets thus acquired by the measuring circuitequals the number of the combinations throughout the entire adjustablerange of the impedance variable devices, i.e. the variable capacitorsVC1, VC2 provided in the impedance matching apparatus 3. In thisembodiment, since the variable capacitors VC1, VC2 are adjustable in onethousand steps, a million sets (1000×1000 sets) of data sets areacquired. When the measurement is performed with respect to two or morefrequencies, a million sets of data sets are acquired with respect toeach frequency.

The S parameter data may be output to a monitor (not shown) of thenetwork analyzer 20, to a display unit or a printer (none shown)provided separately from the impedance matching apparatus 3. Naturally,the data may be output to various external apparatuses (not shown)capable of displaying waveshapes based on analog signals or to anexternal information processing apparatus (not shown) through serialcommunication.

Once the S parameters of the impedance matching apparatus 3 has beenthus acquired, the impedance matching apparatus 3 may be shipped fromthe factory, and incorporated in a high-frequency power supply system ata local site in a configuration as shown in FIG. 1, thus to be put topractical use.

Referring now to FIG. 4 showing functional blocks of the control unit 9and to FIG. 5 showing a flowchart, description will be given on anoperation of the impedance matching apparatus 3 under practical use witha high-frequency power supply system. The control unit 9 includes, fromthe viewpoint of functions, a vectorization unit 21, a forwardwave/reflected wave calculator 22, a first T parameter lookup unit 23, avirtual input reflection coefficient calculator 24, a second T parameterlookup unit 25, a memory 26, and a minimal reflection coefficientidentifier 27, as shown in FIG. 4.

The section including the forward wave/reflected wave calculator 22 andthe first T parameter lookup unit 23 serves as the first calculatoraccording to the present invention. The section including the virtualinput reflection coefficient calculator 24 and the second T parameterlookup unit 25 serves as the second calculator. The reflectioncoefficient identifier 27 serves as the first identifier. The memory 26serves as the second storage unit. Also, the vectorization unit 21constitutes a part of the high-frequency wave information detector.Here, as stated earlier, the directional coupler 6 also constitutes apart of the high-frequency wave information detector according to thepresent invention. In other words, a section including the directionalcoupler 6 and the vectorization unit 21 serves as the high-frequencywave information detector.

When the high-frequency power source 1 supplies the high-frequency wave,the directional coupler 6 separately detects the forward wave and thereflected wave, and outputs the results to the vectorization unit 21.The vectorization unit 21 receives the output of the directional coupler6, and performs sampling of the input signal at a predeterminedinterval, to thereby acquire a forward wave voltage Vfi and a reflectedwave voltage Vri, as vector information including magnitude and phaseinformation of the forward wave (step S1).

It should be noted that the impedance matching apparatus according tothis embodiment includes an A/D converter (not shown) to convert theoutputs of the directional coupler 6 into digital information. Whenemploying an input-side detector in place of the directional coupler 6also, an A/D converter (not shown) is provided to convert the outputs ofthe input-side detector into digital information. Thus, the forward wavevoltage Vfi and the reflected wave voltage Vri can be obtained by aknown method, based on the information input from the input-sidedetector.

When the current forward wave voltage Vfi and the current reflected wavevoltage Vri are output from the vectorization unit 21, they are input tothe forward wave/reflected wave calculator 22 (step S2).

Meanwhile, the position detectors 13, 14 for the variable capacitorsVC1, VC2 detect currently adopted adjustment positions of the variablecapacitors VC1, VC2, and such position information is input to the firstT parameter lookup unit 23 (step S3).

The first T parameter lookup unit 23 reads out the S parameter datastored corresponding to the above-mentioned position information (i.e.the currently adopted adjustment positions), from all of the S parameterdata stored in the EEPROM 15 (Ref. FIG. 2) corresponding to all of thecombinations of the adjustment positions of the variable capacitors VC1,VC2, based on the current position information of the variablecapacitors VC1, VC2 (step S4). The first T parameter lookup unit 23converts the read out set of S parameters into a set of T parameters(step S5), and the prepared set of T parameters is output to the forwardwave/reflected wave calculator 22.

A set of T parameters can be prepared through conversion from a set of Sparameters using the matrix shown as Formula 2, and hence the first Tparameter lookup unit 23 performs calculation according to Formula 2. Ina four-terminal circuit network, in general, it is simpler to utilize Sparameters when measuring transmission characteristics, while it issimpler to utilize T parameters when performing calculation.Accordingly, in this embodiment, S parameters are converted into Tparameters, which are more convenient for calculation. $\begin{matrix}\left. {\frac{1}{S_{12}}\begin{bmatrix}{{S_{11}S_{21}} - {S_{11}S_{22}}} & S_{22} \\{- S_{11}} & 1\end{bmatrix}}\longrightarrow\begin{bmatrix}T_{11} & T_{12} \\T_{21} & T_{22}\end{bmatrix} \right. & (2)\end{matrix}$

Alternatively, T parameters may be prepared when the S parameters of theimpedance matching apparatus 3 is measured before the shipment of theproduct, and then stored in the EEPROM 15 in advance of operation. Inthis case, the first T parameter lookup unit 23 reads out the set of Tparameters corresponding to the adjustment positions of the variablecapacitors VC1, VC2 stored in the EEPROM 15, based on the currentposition information of the variable capacitors VC1, VC2, and outputsthe read out set of T parameters to the forward wave/reflected wavecalculator 22.

Also, instead of the process performed by the first T parameter lookupunit 23, the conversion from S parameters to T parameters may be firstperformed, so as to select the set of T parameters corresponding to thecurrent position information (i.e. currently adopted adjustmentpositions) from all the set of the prepared T parameters, to therebyoutput the selected set of T parameters.

The forward wave/reflected wave calculator 22 calculates a forward wavevoltage Vfo and a reflected wave voltage Vro at the output terminal 3 b,based on the current forward wave voltage Vfi and the current reflectedwave voltage Vri at the input terminal 3 a input thereto at the step S2,as well as based on the T parameter data corresponding to the currentadjustment positions of the variable, capacitors VC1, VC2 (step S6).

In this case, Formula 3 given below is utilized for the calculation ofthe current forward wave voltage Vfo and the current reflected wavevoltage Vro at the output terminal 3 b. In addition, dividing thecurrent reflected wave voltage Vro at the output terminal 3 b by theforward wave voltage Vfo gives the load reflection coefficient Γo.$\begin{matrix}{{\begin{pmatrix}V_{f\quad 0} \\V_{r\quad 0}\end{pmatrix} = {\begin{pmatrix}T_{11}^{\prime} & T_{12}^{\prime} \\T_{21}^{\prime} & T_{22}^{\prime}\end{pmatrix}\begin{pmatrix}V_{f\quad i} \\V_{r\quad i}\end{pmatrix}}}{V_{f\quad 0} = {{T_{11}^{\prime}V_{fi}} + {T_{12}^{\prime}V_{ri}}}}{V_{f\quad 0} = {{T_{21}^{\prime}V_{fi}} + {T_{22}^{\prime}V_{ri}}}}} & (3)\end{matrix}$

Here, T₁₁′, T₂₁′, T₁₂′, and T₂₂′ are the T parameters constituting theset corresponding to the current adjustment positions of the variablecapacitors VC1, VC2. The current forward wave voltage Vfo and thecurrent reflected wave voltage Vro at the output terminal 3 b are outputto the virtual input reflection coefficient calculator 24.

Meanwhile, the second T parameter lookup unit 25 reads out all the Sparameter data stored in the EEPROM 15 with respect to all thecombinations of the adjustment positions of the variable capacitors.VC1, VC2 (Ref. FIG. 6), and converts each of the S parameter data into Tparameters respectively. The prepared T parameters are output to thevirtual input reflection coefficient calculator 24, together with thecorresponding position information (i.e. the information on thecombination of the adjustment positions) of the variable capacitors VC1,VC2.

Also, if the T parameters are to be output from the second T parameterlookup unit 25 in a predetermined sequence, and then the virtual inputreflection coefficient calculator 24 is capable of identifying thecorrespondence between T parameters and the position information of thevariable capacitors VC1, VC2, T parameters alone may be output withoutthe position information of the variable capacitors VC1, VC2corresponding to the T parameters.

Further, as already stated, if T parameters are preinstalled in theEEPROM 15, the second T parameter lookup unit 25 may read out the Tparameter data corresponding to every combination of the adjustmentpositions of the variable capacitors VC1, VC2 from the EEPROM 15together with the position information (i.e. the information on thecombination of the adjustment positions) of the variable capacitors VC1,VC2, and output such data to the virtual input reflection coefficientcalculator 24.

Alternatively, the second T parameter lookup unit 25 may be omitted, andinstead the virtual input reflection coefficient calculator 24 may begranted with a function of reading out the T parameter datacorresponding to every combination of the adjustment positions of thevariable capacitors VC1, VC2 from the EEPROM 15 together with theposition information (i.e. the information on combination of theadjustment positions) of the variable capacitors VC1, VC2.

The virtual input reflection coefficient calculator 24 calculatesvirtual values of input reflection coefficients Γi (hereinafter,“virtual input reflection coefficient Γi″) with respect to everycombination of the adjustment positions of the variable capacitors VC1,VC2, based on the current forward wave voltage Vfo and the currentreflected wave voltage Vro at the output terminal 3 b (step S7).

Specifically, the matrix formula given below as Formula 4 is firstutilized so as to calculate forward wave voltages Vfi′ and reflectedwave voltages Vri′ at the input terminal 3 a corresponding to therespective combinations of the adjustment positions of the variablecapacitors VC1, VC2, based on the current forward wave voltage Vfo andthe current reflected wave voltage Vro at the output terminal 3 b and onthe T parameters corresponding to the respective combinations (Ref. FIG.6) of the adjustment positions of the variable capacitors VC1, VC2output from the second T parameter lookup unit 25. $\begin{matrix}{\begin{pmatrix}V_{fi}^{\prime} \\V_{ri}^{\prime}\end{pmatrix} = {\begin{pmatrix}T_{11}^{''} & T_{12}^{''} \\T_{21}^{''} & T_{22}^{''}\end{pmatrix}^{- 1}\begin{pmatrix}V_{f\quad 0} \\V_{r\quad 0}\end{pmatrix}}} & (4)\end{matrix}$

Here, T₁₁″, T₂₁″, T₁₂″, and T₂₂″ are the T parameters constituting theset corresponding to the adjustment positions of the variable capacitorsVC1, VC2. Accordingly, the virtual input reflection coefficientcalculator 24 reversely calculates from the current forward wave voltageVfo and the current reflected wave voltage Vro at the output terminal 3b into the forward wave voltage Vfi′ and the reflected wave voltage Vri′at the input terminal 3 a using the inversion matrix formula of the Tparameters (T₁₁, T₂₁″, T₁₂″, T₂₂″).

The virtual input reflection coefficient calculator 24 then divides thereflected wave voltage Vri′ by the forward wave voltage Vfi′, thus toobtain the virtual input reflection coefficient Γi as shown in Formula5. The virtual, input reflection coefficient Γi is worked out withrespect to every combination of the adjustment positions of the variablecapacitors VC1, VC2. The virtual input reflection coefficients Γicorresponding to all the combinations of the adjustment positions of thevariable capacitors VC1, VC2 are sequentially transmitted to the memory26 together with the corresponding position information of the variablecapacitors VC1, VC2, to be temporarily stored in the memory 26.$\begin{matrix}{{\Gamma\quad i} = \frac{V_{ri}^{\prime}}{V_{fi}^{\prime}}} & (5)\end{matrix}$

Here, if the virtual input reflection coefficients Γi are to be outputfrom the virtual input reflection coefficient calculator 24 in apredetermined sequence and then at the memory 26 is capableidentification of the correspondence between the virtual inputreflection coefficient Γi and the position information of the variablecapacitors VC1, VC2, the virtual input reflection coefficient Γi alonemay be output without the position information of the variablecapacitors VC1, VC2 corresponding to the virtual input reflectioncoefficient Γi.

The minimal reflection coefficient identifier 27 selects the virtualinput reflection coefficient having the smallest absolute value |Γimin|among the virtual input reflection coefficients Γi corresponding to allthe combinations of the adjustment positions of the variable capacitorsVC1, VC2, calculated by the virtual input reflection coefficientcalculator 24 and stored in the memory 26, and then specifies as atarget position the adjustment positions of the variable capacitors VC1,VC2 corresponding to the absolute value |Γimin| of the selected virtualinput reflection coefficient. For example, when the smallest absolutevalue |Γimin| of the virtual input reflection coefficient is selected atthe point A in FIG. 6, the adjustment position (4, 3) of the variablecapacitors VC1, VC2 is identified as the target position.

In other words, when the variable capacitors VC1, VC2 are adjusted totake the position corresponding to the smallest absolute value |Γimin|of the virtual input reflection coefficient, the amount of the reflectedwave at the input terminal 3 a becomes minimal, and therefore theimpedance can be appropriately matched.

In this embodiment, the minimal reflection coefficient, identifier 27selects the virtual input reflection coefficient having the lowestabsolute value |Γimin| out of the virtual input reflection coefficientsΓi corresponding to all the combinations of the adjustment positions ofthe variable capacitors VC1, VC2. This method is generally equivalent toselecting, when a desired input reflection coefficient (hereinafter,“target input reflection coefficient Γ′”) is zero, a virtual inputreflection coefficient Γi closest to the target input reflectioncoefficient Γ′. The reflection coefficient of zero means that both ofthe real part and the imaginary part of the reflection coefficient arezero, when the reflection coefficient is denoted by the sum of the tealpart and the imaginary part.

The target input reflection coefficient Γ′ may be predetermined in adifferent number, without limitation to zero. In this case, an inputreflection coefficient closest to such target input reflectioncoefficient Γ″ may be selected, out of the virtual input reflectioncoefficients Γi corresponding to all the combinations of the adjustmentpositions of the variable capacitors VC1, VC2. Also, a setting unit thatsets the target input reflection coefficient Γ′ may be provided, so thatthe setting unit may change the target input reflection coefficient Γ′as desired.

For selecting the smallest absolute value |Γimin| of the virtual inputreflection coefficient, the combinations of all the adjustment positionsof the variable capacitors VC1, VC2 may be divided into a plurality ofgroups, and then select the smallest absolute value |Γimin| of thevirtual input reflection coefficient, out of the virtual inputreflection coefficients Γi corresponding to the combinations of theadjustment positions of the variable capacitors VC1, VC2 in a specificgroup, instead of selecting the smallest absolute value |Γimin| of thevirtual input reflection coefficient out of the virtual input reflectioncoefficients Γi corresponding to all the combinations of the adjustmentpositions of the variable capacitors VC1, VC2.

In case that the smallest absolute value |Γimin| of the virtual inputreflection coefficient selected out of the combinations of theadjustment positions of the variable capacitors VC1, VC2 in a specificgroup is not smaller than a predetermined threshold value, the smallestabsolute value |Γimin| of the virtual input reflection coefficient maybe selected out of the combinations of the adjustment positions of thevariable capacitors VC1, VC2 in another group.

The target position information of the variable capacitors VC1, VC2selected by the minimal reflection coefficient identifier 27 istransmitted to the adjustment units 11, 12 (step S8), so that thevariable capacitors VC1, VC2 are displaced to the specified positions bythe stepping motors or the like. In other words, the variable capacitorsVC1, VC2 are adjusted to take the positions that make the virtual inputreflection coefficient Γi minimal.

The foregoing steps cause the capacitances C1, C2 of the variablecapacitors VC1, VC2 to change, so as to match the impedance of thehigh-frequency power source 1 connected to the input terminal 3 a of theimpedance matching apparatus 3 and the impedance of the load 5 connectedto the output terminal 3 b of the impedance matching apparatus 3,thereby supplying a maximal amount of high-frequency power to the load5.

As described above, according to this embodiment the entire of theimpedance matching apparatus 3 is considered as a transmissionapparatus, so as to acquire the transmission characteristics of thetransmission apparatus in a form of information of S parameters and Tparameters throughout the adjustable range of the variable capacitorsVC1, VC2, to thereby perform the impedance matching with higher accuracybased on such information in comparison with the conventional impedancematching method.

To be more detailed, the S parameters and the T parameters represent thetransmission characteristics of the whole matching circuit in theimpedance matching apparatus 3 taking the components of the straycapacitances and the inductances into consideration. Accordingly,adjusting the capacitances C1, C2 of the variable capacitors VC1, VC2 tothe value corresponding to the minimal virtual input reflectioncoefficient calculated based on the transmission characteristics allowsperforming the impedance matching with higher correctness and accuracyin comparison with the conventional impedance matching method.

The foregoing embodiment refers to the impedance matching performed bythe impedance matching apparatus 3 that includes the matching circuitincluding the inductor L1 and the variable capacitors VC1, VC2, inwhich, when the conventional method is employed, the calculation methodof the impedance has to be rearranged according to the circuitconfiguration when the matching circuit has a different configuration.In this embodiment, however, S parameters and T parameters are measuredand calculated with respect to the entirety of the impedance matchingapparatus 3, already affected by the configuration of the matchingcircuit. Therefore, there is no need to rearrange the calculation methodfor each different configuration.

FIG. 7 is a block diagram showing functional blocks of a control unit 9Aof an impedance matching apparatus according to the second embodiment ofthe present invention. The impedance matching apparatus according tothis embodiment is different from that of the first embodiment insetting a desired input reflection coefficient Γ′ in advance,calculating virtual output reflection coefficients Γo′ based on thedesired input reflection coefficient Γ′ and on the T parameter datacorresponding to all the combinations of the adjustment positions of thevariable capacitors VC1, VC2, selecting therefrom the virtual outputreflection coefficient Γo″ closest to the current output reflectioncoefficient Γo, and adjusting the impedance based on the selectedvirtual output reflection coefficient Γo″.

Hereunder, description will be given on an operation of the impedancematching apparatus 3, referring to FIG. 7 showing the functional blockof the control unit 9A and to FIG. 8 showing a flowchart. The controlunit 9A according to the second embodiment includes a vectorization unit21, a forward wave/reflected wave calculator 22, a first T parameterlookup unit 23, an output reflection coefficient calculator 31, a secondT parameter lookup unit 25, a virtual output reflection coefficientcalculator 32, a memory 33, and a reflection coefficient identifier 34.Among the constituents, those of the same numeral as the firstembodiment have the identical functions. The remaining portion of theconfiguration is generally similar to that of the first embodiment.

The output reflection coefficient calculator 31 serves as the thirdcalculator according to the present invention. The section including thevirtual output reflection coefficient calculator 32 and the second Tparameter lookup unit 25 serves as the fourth calculator. The memory 33serves as the third storage unit. The reflection coefficient identifier34 serves as the second identifier.

In the second embodiment, the steps S11 to S16 shown in FIG. 8 aresimilar to the steps S1 to S6 in FIG. 5 showing the operation processaccording to the first embodiment, and hence the following passagescover the steps as from S17. The control unit 9A outputs, once theforward wave/reflected wave calculator 22 calculates the current forwardwave voltage Vfo and the current reflected wave ‘voltage’ Vro at theoutput terminal 3 b (Ref. S16 in FIG. 8), the forward wave voltage Vfoand the reflected wave voltage Vro to the output reflection coefficientcalculator 31.

The output reflection coefficient calculator 31 calculates the currentoutput reflection coefficient Γo at the output terminal 3 b,” based onthe forward wave voltage Vfo and the reflected wave voltage Vro outputfrom the forward wave/reflected wave calculator 22 (step S17). Theoutput reflection coefficient Γo at the output terminal 3 b can becalculated by Formula 6. $\begin{matrix}{{\Gamma\quad o} = \frac{V_{r\quad o}}{V_{f\quad o}}} & (6)\end{matrix}$

The output reflection coefficient Γo at the output terminal 3 bcalculated by the output reflection coefficient calculator 31 is outputto the reflection coefficient identifier 34.

Meanwhile, the second T parameter lookup unit 25 reads out all of the Sparameter data corresponding to all the combinations of the adjustmentpositions of the variable capacitors VC1, VC2 stored in the EEPROM 15,and converts the S parameter data to T parameters. The prepared Tparameters are output to the virtual output reflection coefficientcalculator 32, together with the corresponding position information(i.e. the information on the combination of the adjustment positions) ofthe variable capacitors VC1, VC2.

Here, if the T parameters are to be output from the second T parameterlookup unit 25 in a predetermined sequence, and the virtual outputreflection coefficient calculator 32 is capable of identifying thecorrespondence between the set of T parameter and the positioninformation of the variable capacitors VC1, VC2, the T parameters alonemay be output without the position information of the variablecapacitors VC1, VC2 corresponding to the T parameters.

Also, the T parameters may be prepared when the S parameters of theimpedance matching apparatus 3 are measured before the shipment of theproduct, and stored in the EEPROM 15 in advance of operation.

If the T parameters are preinstalled in the EEPROM 15, the second Tparameter lookup unit 25 may read out the T parameter data correspondingto all the combinations of the adjustment positions of the variablecapacitors VC1, VC2 from the EEPROM 15 together with the positioninformation (i.e. the information about the combination of theadjustment positions) of the variable capacitors VC1, VC2, and outputsuch data to the virtual output reflection coefficient calculator 32.

Alternatively, the second T parameter lookup unit 25 may be omitted, andinstead the virtual output reflection coefficient calculator 32 may begranted with a function of reading out the T parameter datacorresponding to all the combinations of the adjustment positions of thevariable capacitors VC1, VC2 from the EEPROM 15 together with theposition information (i.e. the information on the combination of theadjustment positions) of the variable capacitors VC1, VC2.

It should be noted that the virtual output reflection coefficientcalculator 32 contains a target input reflection coefficient Γ′ which ispreset. Normally the input reflection coefficient Γ′ is set such thatthe amount of the reflected wave at the input terminal 3 a becomesminimal. The target input reflection coefficient Γ′ can be defined byFormula 7. $\begin{matrix}{\Gamma^{\prime} = \frac{Z_{in} - Z_{o}}{Z_{in} + Z_{o}}} & (7)\end{matrix}$

In Formula 7, Zin denotes the target impedance which is the sum of thereal part Rin and the imaginary part Xin, expressed as Zin=Rin+jXin. Zodenotes the characteristic impedance. Also, the virtual outputreflection coefficient calculator 32 may preset the target impedance Zinand the characteristic impedance Zo, to thereby convert these valuesinto the target input reflection coefficient Γ′, instead of directlysetting the target input reflection coefficient Γ′.

The virtual output reflection coefficient calculator 32 calculates thevirtual output reflection coefficient Γo′ at the output terminal 3 b,based on the target input reflection coefficient Γ′ thus set and the Tparameters output from the second T parameter lookup unit 25 (step S18).

Specifically, the virtual output reflection coefficient Γo′ can beobtained by Formula 8. The virtual output reflection coefficients Γo′are calculated with respect to the S parameters (or T parameters)corresponding to all the combinations of the adjustment positions of thevariable capacitors VC1, VC2. $\begin{matrix}{\Gamma_{o}^{\prime} = \frac{T_{21}^{''} + {T_{22}^{''}\Gamma^{\prime}}}{T_{11}^{''} + {T_{12}^{''}\Gamma^{\prime}}}} & (8)\end{matrix}$

Here, T₁₁″, T₂₁″, T₁₂″, and T₂₂″ are the T parameters constituting theset corresponding to the adjustment positions of the variable capacitorsVC1, VC2.

Formula 8 can be led as follows. The virtual output reflectioncoefficient Γo′ can be obtained by dividing the reflected wave voltageVro at the output terminal by the forward wave voltage Vfo, i.e. by theformula of Γo′=Vro/Vfo. The reflected wave and the forward wave voltagesVro, Vfo can be defined as Vfo=T₁₁″·Vfi+T₁₂″·Vri andVro=T₂₁″·Vfi+T₂₂″·Vri respectively, based on Formula 3 and taking the Tparameters into account. (Vfi and Vri are the forward wave voltage andthe reflected wave voltage at the output terminal 3 b.) The above leadsto Γo′=(T₂₁″·Vfi+T₂₂″ ·Vri)/(T₁₁″·Vfi+T₁₂″·Vri). Now, since the inputreflection coefficient Γ′ is defined as Γ′=Vri/Vfi, the formula ofΓo′={T₂₁″·Vfi+T₂₂″·(Γ′·Vfi)}/{T₁₁″·Vfi+T₁₂″·(Γ′·Vfi)}=(T₂₁″+T₂₂″·Γ′)/(T₁₁″+T₁₂″·Γ′)can be established.

The virtual output reflection coefficients Γo′ with respect to all thecombinations of the adjustment positions of the variable capacitors VC1,VC2, calculated by the virtual output reflection coefficient calculator32, are sequentially output to the memory 33 together with thecorresponding position information (i.e. the information on thecombination of the adjustment positions) of the variable capacitors VC1,VC2, to be temporarily stored in the memory 33 (step S19).

Here, if the virtual input reflection coefficients Γo′ are to be outputfrom the virtual output reflection coefficient calculator 32 in apredetermined sequence and at the memory 33 is capable theidentification of the correspondence between the virtual outputreflection coefficient Γo′ and the position information of the variablecapacitors VC1, VC2, the virtual output reflection coefficients Γo′alone may be output without the position information of the variablecapacitors VC1, VC2 corresponding to the virtual output reflectioncoefficients Γo′.

The reflection coefficient identifier 34 selects the virtual outputreflection coefficient Γo″ that is the closest to the output reflectioncoefficient Γo at the output terminal 3 b output from the outputreflection coefficient calculator 31, out of the virtual outputreflection coefficients Γo′ corresponding to all the combinations of theadjustment positions of the variable capacitors VC1, VC2, calculated bythe virtual output reflection coefficient calculator 32 and stored inthe memory 33.

For example, a reflection coefficient can be expressed as the sum of areal part and an imaginary part (r=u+jv, where u is the real part and vis the imaginary part), and hence distances between the reflectioncoefficients on the uv coordinates can be easily obtained. Specifically,when the output reflection coefficient Γo is defined by uo+jvo, and thevirtual output reflection coefficient Γ1 is defined by u1+jv1 as shownin FIG. 9, the distance between these reflection coefficients L1 on theuv coordinates can be obtained from L1=√{(uo−u1)²+(vo−v1)²}.

Also, the distance L2 between the virtual output reflection coefficientΓ2 (u2+jv2) other than the virtual output reflection coefficient Γ1 andthe output reflection coefficient Γo can be obtained fromL2=√{(uo−u2)²+(vo−v2)²}. Accordingly, it is appropriate to select thevirtual output reflection coefficient corresponding to the shorterdistance (in this case Γ2) out of L1, L2 as the virtual outputreflection coefficient Γo″ closest to the output reflection coefficientΓo.

The reflection coefficient identifier 34 then identifies as the targetposition the adjustment position of the variable capacitors VC1, VC2corresponding to the selected virtual output reflection coefficient Γo″.For example, when the selected virtual output reflection coefficient Γo″has the adjustment position on the point A in FIG. 6, the adjustmentposition (4, 3) of the variable capacitors VC1, VC2 is identified as thetarget position.

In other words, when the variable capacitors VC1, VC2 are adjusted totake the position corresponding to the virtual output reflectioncoefficient Γo″ closest to the output reflection coefficient Γo at theoutput terminal 3 b, the reflection coefficient becomes closest to thepreset target input reflection coefficient Γ′. Since the target inputreflection coefficient ΓΔ is normally a minimal value i.e. zero (Γ′=0+j0when the target input reflection coefficient Γ′ is expressed as the sumof the real part and the imaginary part), adjusting the variablecapacitors VC1, VC2 as above enables reducing the reflected wave at theinput terminal 3 a to the minimal amount when performing the impedancematching. It is a matter of course that, as is the case with the firstembodiment, the target input reflection coefficient Γ′ may be set at avalue other than zero. Also, a setting unit that sets the target inputreflection coefficient Γ′ may be provided, so that the setting unit maychange the target input reflection coefficient Γ′ as desired.

The target position information of the variable capacitors VC1, VC2selected by the reflection coefficient identifier 34 is transmitted tothe adjustment units 11, 12 (step S20), so that the variable capacitorsVC1, VC2 are displaced to the specified position. In other words, thevariable capacitors VC1, VC2 are adjusted to take a position that makesthe virtual input reflection coefficient Γi minimal.

As described above, according to the second embodiment the impedancematching apparatus 3 is utilized as a transmission apparatus as a whole,so as to acquire the transmission characteristic of the transmissionapparatus in a form of the information on the S parameter and the Tparameter with respect to the adjustable range of the variablecapacitors VC1, VC2, to thereby perform the impedance matching based onsuch information. Such method allows performing the impedance matchingwith higher accuracy in comparison with the conventional impedancematching method.

Also, since the target input reflection coefficient Γ′ is preset, thevirtual output reflection coefficient calculator 32 only has tocalculate once the virtual output reflection coefficient Γo′corresponding to all the combinations of the adjustment positions of thevariable capacitors VC1, VC2, unless the target input reflectioncoefficient Γ′ has to be modified after activating the system. Thecontrol unit 9 according to the first embodiment has to calculate in thevirtual input reflection coefficient calculator 24 the forward wavevoltage Vfi′ and the reflected wave voltage Vri′ at the input terminal 3a each time the load fluctuates, while such calculation has only to beperformed once according to the second embodiment, and therefore thecalculation load can be significantly reduced. Further, the secondembodiment does not utilize the inversion matrix formula of the Tparameter unlike the first embodiment 1, thus saving the memory regioncorresponding to the inversion matrix formula of the T parameter.

It is evident that the scope of the present invention is not limited tothe foregoing embodiments. For example, while the S parameter and the Tparameter are employed as the characteristic parameter for thefour-terminal circuit network in the embodiments, the characteristicparameter is not limited thereto. A Z parameter or a Y parameter may beemployed as the characteristic parameter, in which case such parametermay be converted to the T parameter for performing the impedancematching.

Further, while the foregoing embodiments refer to the impedance matchingapparatus 3 that includes the reverse L-shaped matching circuitincluding the inductor L1 and the variable capacitors VC1, VC2, theconfiguration of the matching circuit is not limited to that employed inthe embodiment, but may be of a n-shape, a T-shape, an L-shape and soforth. In addition, a variable inductor may be employed as the impedancevariable device, instead of the variable capacitor.

Although the present invention has been described as above, it isapparent to those skilled in the art that various modifications may bemade without departing from the spirit and scope of the presentinvention, and that such modifications are included in the appendedclaims.

1-4. (canceled)
 5. An impedance matching apparatus to be interposedbetween a high-frequency power source and a load, for changing animpedance of an impedance variable device so as to match an impedance ofthe high-frequency power source and an impedance of the load,comprising: a high-frequency wave information detector to detectinformation on a forward wave advancing from the high-frequency powersource toward the load and information on a reflected wave advancingfrom the load toward the high-frequency power source, at an inputterminal of the impedance matching apparatus; a variable deviceinformation detector to detect information on a variable value of theimpedance variable device; a first storage unit to store therein acharacteristic parameter of the impedance matching apparatus acquiredthrough a preceding measurement, with respect to the information on avariable value of a plurality of the impedance variable devices, incorrelation with the information on the variable value of the impedancevariable device; a first calculator to calculate the information on theforward wave and the information on the reflected wave at an outputterminal of the impedance matching apparatus, based on the informationon the variable value of the impedance variable device detected by thevariable device information detector, on the characteristic parameterstored in the first storage unit, and on the information on the forwardwave and the information on the reflected wave detected by thehigh-frequency wave information detector; a third calculator tocalculate a reflection coefficient at the output terminal of theimpedance matching apparatus, based on the information on the forwardwave and the information on the reflected wave at the output terminal ofthe impedance matching apparatus calculated by the first calculator; afourth calculator to calculate a reflection coefficient at the outputterminal of the impedance matching apparatus with respect to theinformation on the variable value of the plurality of impedance variabledevices, based on a predetermined target input reflection coefficientand a plurality of the characteristic parameters stored in the firststorage unit; a third storage unit to store therein a plurality of thereflection coefficients calculated by the fourth calculator incorrelation with the information on the variable value of the impedancevariable device; a second identifier to select a reflection coefficientclosest to the reflection coefficient at the output terminal of theimpedance matching apparatus calculated by the third calculator out ofthe plurality of reflection coefficients stored in the third storageunit, and to identify the information on the variable value of theimpedance variable device corresponding to the selected reflectioncoefficient; and an adjustment unit to adjust an impedance of theimpedance variable device, based on the information on the variablevalue of the impedance variable device identified by the secondidentifier.
 6. The impedance matching apparatus according to claim 5,further comprising a setting unit to set the target input reflectioncoefficient.
 7. The impedance matching apparatus according to claim 5,wherein the characteristic parameter is an S parameter, or a T parameteracquired through conversion from the S parameter.